3 ideas
The king realizes his realm is being drained the same way, traces the rot to his trusted vizier Rast-Ravish, who has been colluding with enemies and extorting subjects, and executes him. The lesson is that the most damaging threat is the trusted guardian who has quietly made terms with the predator, not the predator itself.
Because officials know any peasant can reach the king directly, the credible threat of exposure restrains their abuses more than rules alone would. Removing the gatekeepers between ruler and ruled is therefore the core check on delegated power.
A ruler must keep reliable intelligence agents and couriers reporting on governors, tax collectors, and judges, so that he knows of misconduct before it spreads. Ignorance of what agents are doing is itself a ruler's failure, because unchecked officials oppress the people and the people's ruin destroys the treasury and the state.